Method and means for the thermic treatment of metals, chiefly of light alloys



Oct 10, 1950 1'. BOSTROEM 2,525,203

METHOD AND MEANS FOR THE THERMIC TREATMENT 0F 7 METALS CHIEFLY OF LIGHT ALLOYS 2 Sheets-Sheet 1 Filed Feb. 26, 1946 gwuc/Mov Th soda/"e Baa/r6602 Oct. 10, 1950 T. BOSTROEM 25,

METHOD AND MEANS FOR THE THERMIC TREATMENT OF METALS CHIEFLY OF LIGHT ALLOYS Filed Feb. 26, 19,46 2 Sheets-Sheet 2 Theodore Basfroem- Patented Oct. 10, 195

METHOD AND MEANS FOR THE THERMIC TREATMENT OF METALS, CHIEFLY OF LIGHT ALLOYS Theodore Bostroem, Paris, France Application February 26, 1946, Serial No. 650,283 In France February 28, 1945 11 Claims,

The present invention has for its primary object the heating of metal articles, more particularly strip, bar, wire, tube, structural and other sections of indefinite length as well as separate comparatively short metal articles in view of their heat treatment (such as annealing, tempering, hardening, etc.), by passing them in a continuous manner through a bath comprising at least two nonmiscible substances, of which at least one has a specific weight higher than the articles to be treated whereas at least one other will have a specific gravity lower than said articles, so that said articles will float over the first substance or substances and will be covered by the second.

Owing to this particular composition of the bath, it is possible to pass the articles in a continuous manner through the bath, by making them enter the bath through one side and then glide over the surface of the heavier substance or substances forming the bath, on which surface the articles to be treated will float before extraction at the other end of the bath. However, owing to the fact that the articles to be treated enter the bath in a relatively cold condition, it is preferable to heat them up rapidly before the heat treatment proper begins. Therefore another feature of the method consists in passing the articles to be treated through a preheating bath, which forms preferably a zone or compartment of the main bath. Moreover, by reason of the softening of the metal of the articles to be treated while remaining at soaking temperature, it is preferable to slightly cool the articles before extracting them from the bath in order to facilitate their handling. Therefore, my invention covers also a preliminary cooling step performed preferably in a separate zone or compartment of the main bath, during which the alloy to be quenched is sufficiently cooled to permit its handling through adequate transportation devices but not enough to allow for a precipitation of its ingredients.

The vat for carrying out this improved method is therefore constituted by an elongated receiver comprising three zones or compartments, to Wit:

(a) An entrance zone or compartment inside which the articles are energetically heated;

(b) A main zone or compartment occupying the major part of the receiver, inside which the desired treatment is applied to the articles at the proper temperature or temperatures;

(0) A preliminary cooling zone or compartment operating just before the articles move out of the bath in order to be quenched, a sufficient drop of temperature being provided in said cooling zone or compartment for allowing the easy handling of the cooled articles.

If the articles to be treated are of indefinite length, as in the case of strips, wires, etc., appropriate unwinding devices are used on the entrance side of the bath, whereas rewinding devices are used on its output side. The entrance unwinding device may push the product into the bath and on to the surface of the heavy bath component, whereas the exit rewinding device will pull the product out of the bath, the product being then sufiiciently cooled to withstand such handling. The entrance and exit handling devices may consist of rollers, belts, chains or the like.

There is no limitation as to the choice of the substances making up the bath for the method considered, provided, however, that the following condition are observed: they should not be miscible with one another, they should be chemically and physically sufficiently neutral with reference to one another, to the articles to be treated and preferably towards the substance forming the bath receiver; the substance or substances which are located at the bottom of the bath should have a higher specific gravity than the metal of the articles to be treated, whereas the substance or substances forming the upper part of the bath, which are in a liquid or aeriform state should have a lower specific gravity than the metal of the articles to be treated, so that the latter will float and glide on the surface of the heavier liquid of the bath bottom and are covered by the layer or layers forming the upper part of the bath.

According to a particular form of execution of the invention, the lower bath component is constituted by molten lead, whereas the remainder of the bath is filled by a molten simple or compound salt, which is chemically and physically neutral with reference to lead and the metal forming the articles under treatment at temperatures up to and slightly above the temperature of the heat treatment considered.

The bath is thus constituted by a preferably three-compartment tank provided with a cover and comprising inside and/or outside it elements for temperature control; 1. e. heating or cooling elements located under and over the product passing through the bath, i. e. inside one of the substances as well as the other.

These thermic control elements may be of any desired type, their choice depending on various considerations. However, according to a preferred form of execution, these elements are constituted by tubes immersed in both the lead or the like lower portion as in the upper salt portion of the bath, through which tubes a more or less hot fluid circulates according to the necessity of heating more or less the part of the bath corresponding thereto.

According to a further feature of my invention, the fluid circulating through said tubes is constituted by the same substance as that wherein the tubes are immersed, which allows bringing a very simplified solution to the problem of the fluid-tightness between the tubes and the bath.

In order to provide a rapid, uniform and easily adaptable adjustment of the temperature, the fiuid is caused to circulate through the tubes at a speed which is sufficiently high for the diiferences in temperature at the inlet and the outlet of any tubes considered to be sufficiently low for avoiding any substantial difference in temperature between the two sides of the bath. The advantage of such a method of indirect adjustment of the temperature of the bath resides in the fact that the surface of the two superposed baths remains absolutely calm and free of agitation, which allows providing for a minimum difference in level and thereby making use of a layer of salt of small depth over a well filled bath, which leads to a great reduction in the straining of the products as they leave the bath.

According to another object of my invention, I may use for the overlying fluids specific gravities which are different in the three zones or compartments. As a matter of fact, in the inlet and outlet compartments, said fluids should have a greater specific gravity in order to better support the strip of metal whereas in the central compartment said overlying fluid should have a specific gravity as low as possible so that the strip may be borne as much as possible by the molten metal.

According to a still further object of my invention, the differences between the ideal treating temperature prevailing in the principal compartment or soaking zone and the temperature which it is desired to obtain respectively in the inlet and outlet compartments should be determined in accordance with the speed of displacement of the products to be treated and to their thickness. This diiference in temperature is adapted, as concerns the inlet zone or compartment, to allow the product to be treated to be raised rapidly to the ideal temperature, while the drop in temperature provided in the outlet compartment or zone should be suflicient to restore as rapidly as possible the mechanical resistance required for allowing its handling with the apparatuses arranged at the outlet of the bath. Moreover as the major part of the heat is communicated to the strip in the entrance zone, the heating of the central zone is necessary only for compensating the losses through heat radiation, the heating elements of the entrance zone being thus much more powerful than those of the central zone; as to the tubular heat exchanging elements or the like provided in the outlet zone, they are mainly cooling members providing for the desired reduction in the temperature of the products treated.

It should be noticed that, by reason of the manner of circulating the products under treatment, the bath may be provided with a cover permanently secured over the same and including the desired thermic circulation which was impossible in the case of the prior baths. Such a cover provides the advantage of considerably reducing the losses of heat through radiation, which leads to a considerable economy in heat.

Among the further advantages of my invention, not mentioned hereinabove, I may mention that there is practically no warping in the quenching.

Furthermore, my invention has for its object a liquid bath on the surface of which the parts to be treated float and which receives a circulating movement which is such that the particles of the liquid bath lying in proximity with its upper layer 4 move in the direction in which it is desired to make the objects under treatment progress.

Thus it is possible to obtain a perfect equilibrium in temperature between the bath and the objects under treatment. Moreover the movement of the liquid has for its action to cooperate in the driving of said objects, which is of considerable advantage in the case of endless bodies and is even indispensable in the case of a succession of separate objects.

Obviously this circulation may be executed without widening thereby the scope of my invention. Thus for instance the circulation may be obtained through any suitable mechanical means.

However it is preferable to execute this circulation through thermic means by heating the liquid in any suitable manner so as to form a thermosyphon.

In a preferred form of construction of the bath container therefor the bath has in vertical longitudinal cross-section an annular shape of any suitable configuration.

I may also heat the bath through induction, this induction heating means being associated with such a bath container having a longitudinal annular cross-section. In this case, the bath proper for instance may be provided with a downwardly directed connection opening into a lower horizontal part connected again with the main bath through an upwardly directed connection and this bath container forms the one coil secondary of a transformer, the primary coils of which are suitably fed with current and the two primary and secondary windings of which are coupled through a common magnetic core.

According to a further feature of the invention, the cross-section of such an annular bath container is not uniform and whereas the upper part including the level bearing the objects to be treated has a, wide and flat cross-section, I may use a circular or substantially square cross-section of much smaller area for the lower arm and the rising connection; on the contrary the downwardly directed arm should have a cross-section approximating that of the upper part. It will be readily understood that with such an arrangement the secondary current generated in the annular bath will heat more considerably the parts having a smaller cross-section area so as to produce a thermo-syphon effect which forces the liquid, say molten lead, to progress in the desired direction.

It is possible to provide for the heating considered by means of polyphase current in which case the lower horizontal arm and part of the upwardly directed connection should be subdivided into a number of passages equal to the number of phases considered. Thus, no current need flow through the upper part of the bath container and the downwardly directed connection thereof;

for starting the heating of such a bath a special arrangement may be provided such as a common one-phase winding, a relay ensuring the temporary switching oil of one phase, independent heating means or the like, said special arrangement being used until the whole lead bath is molten and the thermosyphon. begins to operate.

Any other direct or induction heating means may be used as the example described is given out solely by way of indication and by no means in a limitative manner.

In the case of an aeriform fluid forming the upper layer overlying the heavy liquid carrying the products under treatment, perfect gas-tightness is required at the points at which the endless strip or the like product enters the bath container and passes out of same.

Moreover I have found that it is important to give the strip as it enters the bath a suitable predetermined direction and curvature. In fact, I may provide rollers at the entrance into the bath associated with means for varying the slope of the strip at the point of contact with the bath and on the other hand its curvature at the same point.

My invention will be better understood by means of the accompanying drawings illustrating solely by way of example and defining forms of execution of my invention.

In said drawings:

Fig. l is a vertical cross-section of a bath,

Fig. 2 is a diagram of the temperatures,

Fig. 3 is a cross-section through line III-III of Fig. l.

Fig. 4 is a cross-section showing the means for feeding the thermic adjustment elements,

Fig. 5 is a vertical cross-section of a bath the cross-section of which is annular,

Fig. 6 is a vertical view through line VI-VI of Fig. 5.

Fig. 7 is a cross-section similar to Fig. 5 for the case of an induction heated bath,

Fig. 8 is a partial cross-section through line VIII-VIII of Fig. 7, and

Fig. 9 is a partial cross-section showing the rollers guiding the strip to be treated into the bath.

Reverting first to Figs. 1 and 2, l designates a container for the bath, subdivided into three compartments A, B and Cor more zones as the case may be. 2 designates the part of the receiver filled with molten lead, 3 the part filled with salt or an aeriform layer and 4 the cover. I designates the elements adapted for providing thermic adjustments. The strip to be treated 9 is unwound ofif aspool 5 and is urged by a set of rollers 6 into the bath. It is submitted inside the first zone or compartment A to a speedy heating as shown by the full drawn lines shown diagrammatically in Fig. 2 illustrating graphically the temperature of the strip as it passes through the bath container. The dotted line in said Fig. 2 shows the temperature of the bath at correspond-- ing points of the progress of the strip. In the compartments B the temperature of the strip and of the bath are the same and the two lines are superposed. As it passes out of the compartment A, the strip passes into the compartment B where it floats over the surface of the molten lead while it is covered by the salt layer (or a neutral seriform atmosphere as the case may be). The strip is then drawn out through a system of rollers 8 after a preliminary cooling in the compartment or zone C as the case may be, said cooling being sufiicient for the strip to acquire a sufiicientmechanical resistance which allows its handling through said roller or the like means. The thermic adjusting elements I are constituted in the example illustrated by tubes inside which fiows preferably a current at the desired temperature of the same substance as that inside which said tubes are immersed;

In Fig. 4, I have shown diagrammatically a circulation circuit wherein a pump l0 forces fiuid in the direction of the arrow and causes it to pass through a reservoir l2 inside which the temperature of the liquid is increased or reduced through auxiliary heat regulating elements H. The strip of material under treatment may be cooled at the outlet from the bath for instance through spraying or blowing at the point shown 6 by the arrow [3 or brought in contact with a. colder body.

Referring now to Figs. 5 and 6, I designates again the bath and 4 the cover therefor, said cover being adapted in this case to provide for the required fluid-tightness so that the upper space 14 above the level of the heavy liquid bath 2 may be filled with an aeriform fluid. The fluid-tightness at the entrance and at the outlet of the endless strip or the like is provided by suitably mounted rollers 6 and 8 respectively at the inlet and at the outlet. The strip is drawn out of the bath at I3 through any suitable means. In the case illustrated the strip is drawn out of the bath vertically so as to reduce the straining thereof.

In the case of Figs. 5 and 6, the longitudinal vertical cross-section of the bath is ring-shaped, which allows providing a circulation of the liquid in the direction of the arrow in order that said liquid may move in the vicinity of its upper level in. the same direction as the strip 9. As disclosed hereinabove this circulation may be ensured in any suitable maner and in particular though,

mechanical or thermic means.

In the example illustrated in Figs. 5 and. 6, thiscirculation is ensured mechanically as shown dia-- grammatically by a propeller may be ensured in any suitable manner for instance by heating tubes or'the like elements 1.]

In the example of Figs. 5 and 6 the transversal. width of the ring shaped container is substantiaily uniform throughout its periphery, as illus trated by Fig. 6.

On the contrary in the example illustrated in.

Figs. 7 and 8 this width differs in the upper and the lower part of the bath container, as apparent in the cross-section of Fig. 8. In this case, the cross-section of the ring occupied by the circulating liquid is wide and shallow in the upper portion thereof while it has a very small crosssection area and a reduced rectangular square,:

. for the cross-section oi"; the upwardly directed.

arm through which the molten lead or the likeliquid arises to have a smaller area than the: connection inside which the liquid moves downwardly.

In Fig- 9, I have shown the arrangement for the adjustment at will of the angle of engagemerit of the strip as it enters into contact with: the layer of heavy liquid,said adjustment being, associated with an adjustment of the curvatureof the strip.

weight, 9 the strip advancing in floating relationship with said liquid and H! the lighter fluid overlying the strip.

With a view to modifying the angle of engagement of the strip .3 coming into contact with the: bath level, the pinch-rolls holding said strip: are carried by a common support adapted to rock; round the axis 0 lying in the plane of the axes of said pinch-rolls shown respectively at X and The heating In said Fig. 9, i still designates the wall of the bath, 2 the liquid of a high specific Z, the amplitude of the rocking movement being shown for instance at 1). Furthermore, in order to modify the curvature R of the strip, there is arranged a small auxiliary roller [9 carried by an arm 20 pivotally secured to an axis alined with that X of a lower roller 6. By causing the arm 20 to rotate round its pivoting axis, for instance through an angle a it is possible to displace the axis Y of the roller [9 so as to modify the curvature of the strip.

Obviously, the specific execution of the bath receiver, its subdivision, size and shape, the manner of driving the objects under treatment and the like elements of the device executed in accordance with my invention may be chosen at, will without widening thereby the scope of my invention. It should also be noticed that my improved process although it is particularly intended for the treatment of endless products, such as strips, wires, bars, tubes and the like, may also be advantageously applied to the treatment of non-continuous objects, said objects being introduced in the bath through its inlet end and advancing over the bath through the agency of any suitable means and being finally removed through the outlet end. Lastly, as disclosed, the substance forming the bath may also vary according to the case as also the means for heating said bath, the location, number and shape of such heating means, and so on.

What I claim is:

1. A method of heat treatment of metallic bodies which consists in conveying said bodies at the interface between two superposed layers forming a bath, said layers being composed of substances each immiscible with and substantially inert to each other and to the metal being treated, said immiscible substances varying in specific gravity, the heavier of which forms the lower layer and is heavier than the metal being treated which tends to float thereon and is liquid at the temperature of heat treatment, and the lighter substance comprising said bath being lighter than the metal being treated so as to form an inert seal thereabove and protectively cover the metal while passing the same through the bath for heat treatment.

2. A method of continuous heat treatment of light metallic bodies comprising continuously passing the metal through a series of three zones,

the first zone being maintained at a temperature sufiicient to preheat the metal passing therethrough, the second zone comprising a soaking zone wherein the metal passing therethrough is maintained for a time and at a temperature sufficient to dissolve the components thereof to a solid solution, and the third zone being maintained at a temperature lower than the first two zones suificient to reduce the temperature of the metal to a suitable handling temperature without precipitating the components of the metal, each of said zones comprising a bath formed by two superimposed layers of non-miscible substantially inert substances, the lowermost layer being heavier than the metal being treated which tends to float thereon and is liquid at the temperature of heat treatment, and the lighter substance comprising said bath being lighter than the metal being treated so as to form an inert seal thereabove and protectively cover the metal while passing the same through the bath for heat treatment, and continuously passing said metal through said series of heat treatment zones while floating on the surface of said heavier component without tension.

3. The method as defined in claim 1 wherein the heat treatment is performed continuously upon a continuous light metal strip material.

4. The method as defined in claim 1 wherein one of the immiscible bath layers is a fused salt.

5. The method as defined in claim 1 wherein the heavier layer of the bath is a molten heavy metal.

6. The method as defined in claim 1 wherein the lighter component of the bath is a gas.

7. The method as defined in claim 1 wherein the heavier layer of the bath is molten lead and the lighter component of the bath is a fused salt floating thereon.

8. The me hod is defined in claim 1 wherein the lighter layer of the bath is a gas and the heavier layer is molten lead.

9. A metal heat treating device comprising an elongated vat having an inlet and an outlet at opposite ends containing two superposed nonmiscible substances, the underlying substance being liquid at operating temperature, means within the vat to continuously circulate said underlying substance from the inlet to the outlet of said vat, said means forming a liquid conveyor of high gravity, means to feed metallic bodies to be heat treated through the inlet of said vat, and means to continuously guide said metallic bodies upon the underlying substance at the interface between the supeposed substances and through the outlet of said vat.

10. A metallic heat treating device comprising an elongated vat, subdivided in three adjacent and communicating compartments adapted to contain at least two non-miscible substances of different specific gravity, the underlying substance being liquid at operating temperature, said vat having an inlet and an outlet at opposite ends, means within the vat to continuously circulate the liquid substance, means to continuously feed metallic bodies to be heat treated through the inlet of said vat and to pass said metallic bodies over the surface of said liquid substance, the underlying liquid bath forming a liquid conveyor of hi h gravity, means to continuously guide said metallic bodies through the outlet of said vat without applying thereon any tensile or drawing stress, means in the inlet and in the intermediate compartments for continuously heating the two superposed substances of the bath in the inlet compartment and only the underlying substance in the intermediate compartment, and means for continuously cooling the two superposed bath substances in the outlet compartment.

11. Device according to claim 10 in which the heating means are of the electric inductive type.

THEODORE BOSTROEM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,022,372 Hopkins Nov. 26, 1935 2,036,563 Beck Apr. 7, 1936 2,166,364 Michel July 18, 1939 2,303,132 Murray et al Nov. 24, 1942 2,416,378 Chandler et a1. Feb. 25, 1947 

